initial drop: Dialectic.PlexumPlugin v0.1

Port of Dialectic.OpenclawPlugin to the Plexum SDK. 8 dialectic_*
tools wired to Dialectic.Backend over HTTP:

  list_topics, topic_detail, list_arguments, propose_topic,
  signup, post_argument, submit_verdict, view_verdict

Differences from the OpenClaw port worth noting:

  - Per-agent API key storage: OpenClaw used secret-mgr (one entry
    per agent's keyspace). Plexum has no secret-mgr; v1 stores
    keys directly in plugin config (apiKey + agentKeys map).

  - Agent identity at tool dispatch: OpenClaw framework surfaces
    ctx.agentId; Plexum SDK doesn't yet plumb the calling agent
    through ToolPlugin.CallTool. v1 falls back to
    config.defaultAgentID — same stop-gap HarborForge.PlexumPlugin
    is on. Tracked as upstream SDK work.

  - HF on_call coverage pre-check on signup: stub that always
    returns "skipped", matching OpenClaw v1's behavior (HarborForge
    never shipped the cross-plugin coverage query). pre_validated
    is sent as false so the backend records audit honestly.
    DIALECTIC_PLUGIN_BYPASS_HF=1 env retains parity with OpenClaw.

  - Activation: lazy (no background services, unlike HarborForge's
    eager-spawn for the calendar scheduler + monitor bridge).

Backend client follows the bearer-auth contract OpenClaw's
backend-client.ts established; endpoint shapes are unchanged.

internal/backend/client.go

@@ -0,0 +1,105 @@
+// Package backend is the typed HTTP client for Dialectic.Backend's API.
+// Endpoint shapes mirror Dialectic.OpenclawPlugin/plugin/src/backend-client.ts
+// so the two plugins drop into the same backend without per-plugin
+// adapters.
+package backend
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+	"strings"
+	"time"
+)
+
+type Client struct {
+	BaseURL string
+	APIKey  string
+	HTTP    *http.Client
+}
+
+func New(baseURL, apiKey string) *Client {
+	return &Client{
+		BaseURL: strings.TrimRight(baseURL, "/"),
+		APIKey:  apiKey,
+		HTTP:    &http.Client{Timeout: 15 * time.Second},
+	}
+}
+
+func (c *Client) Get(ctx context.Context, path string) (json.RawMessage, error) {
+	return c.do(ctx, http.MethodGet, path, nil)
+}
+
+func (c *Client) Post(ctx context.Context, path string, body any) (json.RawMessage, error) {
+	return c.do(ctx, http.MethodPost, path, body)
+}
+
+func (c *Client) Put(ctx context.Context, path string, body any) (json.RawMessage, error) {
+	return c.do(ctx, http.MethodPut, path, body)
+}
+
+func (c *Client) do(ctx context.Context, method, path string, body any) (json.RawMessage, error) {
+	if c.APIKey == "" {
+		return nil, errors.New("dialectic api key not configured — set plugins.dialectic.config.apiKey or agentKeys[<agent_id>]")
+	}
+	url := c.BaseURL + ensureLeadingSlash(path)
+	var rdr io.Reader
+	if body != nil {
+		raw, err := json.Marshal(body)
+		if err != nil {
+			return nil, fmt.Errorf("marshal %s %s: %w", method, path, err)
+		}
+		rdr = bytes.NewReader(raw)
+	}
+	req, err := http.NewRequestWithContext(ctx, method, url, rdr)
+	if err != nil {
+		return nil, err
+	}
+	if body != nil {
+		req.Header.Set("Content-Type", "application/json")
+	}
+	req.Header.Set("Authorization", "Bearer "+c.APIKey)
+	req.Header.Set("Accept", "application/json")
+
+	res, err := c.HTTP.Do(req)
+	if err != nil {
+		return nil, fmt.Errorf("%s %s: %w", method, path, err)
+	}
+	defer res.Body.Close()
+	raw, _ := io.ReadAll(res.Body)
+	if res.StatusCode < 200 || res.StatusCode >= 300 {
+		return nil, fmt.Errorf("%s %s → %d: %s",
+			method, path, res.StatusCode, truncate(raw, 500))
+	}
+	if len(raw) == 0 {
+		return nil, nil
+	}
+	return raw, nil
+}
+
+func ensureLeadingSlash(p string) string {
+	if strings.HasPrefix(p, "/") {
+		return p
+	}
+	return "/" + p
+}
+
+func truncate(b []byte, n int) string {
+	if len(b) <= n {
+		return string(b)
+	}
+	return string(b[:n]) + "…"
+}
+
+// TopicDetail is the minimal shape the signup tool needs (debate window
+// for HF pre-check). The Dialectic backend returns more fields — they
+// pass through untouched in the raw JSON the tools surface to agents.
+type TopicDetail struct {
+	ID            string `json:"id"`
+	DebateStartAt string `json:"debate_start_at"`
+	DebateEndAt   string `json:"debate_end_at"`
+}